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03-13-2019, 08:41 PM | #1 |
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Mitchell transmission or overdrive
I would like to improve the drivability of my 31 closed cab pickup. Originally I was thinking about a Mitchell overdrive but now I’m wondering if I would be better off with the Mitchell synchromesh transmission. The truck has a strong engine and 3.56 rear end and 19 inch wheels. Most of our touring is at 45 to 50 we seldom run much higher. Our terrain is flat to rolling hills. My thinking is that the 3.56 rear end gets us going fast enough, seems like it would be great to have the easy up and down shifting from a synchronized transmission. I know this transmission is only synchronized in 2nd and 3rd gears that’s what I’m used to with my 40’s vintage cars. I wonder about your experience with either the transmission or overdrive and what other factors I might be overlooking. I have read as many past threads as I could find and am still pondering.
Thanks Bill Last edited by bill boz; 03-14-2019 at 06:42 AM. |
03-13-2019, 09:14 PM | #2 |
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Re: Mitchell transmission or overdrive
Buy the overdrive..actually its a splitter box,the first time your wring out second low and shift to second high you'll be sold.
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03-13-2019, 09:27 PM | #3 |
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Re: Mitchell transmission or overdrive
I have one car with both the MItchell transmission and O/D. We do lots of miles towing a camper behind that one. I have another 3 cars and all of those have the original cog house and a Mitchell O/D (gear splitter). One of those also has a 3.54 rear end (1928 Tudor) with a B engine fitted with a downdraught carby. That car doesn't handle hills all that well but I can sit on 60 mph easily enough in it on the flat. I think I prefer the standard rear end with O/D. The original gearbox is fine.
In your case, I'd go the O/D
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03-13-2019, 10:57 PM | #4 |
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Re: Mitchell transmission or overdrive
I think you mean 2nd and 3rd.
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03-14-2019, 12:11 AM | #5 |
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Re: Mitchell transmission or overdrive
I have the F150 OD with 3.78 rear. This gives me Synchronized gears plus OD. Does very well on the flat or hills.
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03-14-2019, 04:41 AM | #6 |
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Re: Mitchell transmission or overdrive
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This is a nice car to drive, but every now and then on really steep 180 degree uphill bends needs first gear to avoid straining. On the other hand on long uphill pulls in the hills where top gear is too high, overdrive second really speeds things up. Our Roadster with a very strong engine cannot go as fast up these hills where second gear is needed without going over my 2600 rev limit. But it pulls the very tight uphill bends in second gear ok. It has 19 inch wheels with Excelsior sport radials 155X19. Gearbox is standard Model A, overdrive is 26% Mitchell and rear end 3.78. Both are a delight to drive and impossible to say which is best. Reading this to myself I think the message is stay with 3.78, put in 26% Mitchell o/d and if your gearbox needs any kind of attention put in the Mitchell synchro internals. For a strong engine ( higher compression, better camshaft, larger carb.) go for higher first and second gear ratios. For a standard engine I am not sure on this last point. One can up the ratio on either or none of first and second gears. I put a plus 15% first and second in a friends cabriolet with standard diff and tyres. His only comment is "it goes very fast in reverse now, especially in backing out of my shed". He is 85 and a rather slow driver. SAJ in NZ Last edited by SAJ; 03-14-2019 at 03:51 PM. Reason: Changed 12% to15% |
03-14-2019, 06:41 AM | #7 |
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Re: Mitchell transmission or overdrive
I have the 3.54 rear with the Mitchell synchro tranny, was going to get the overdrive, but don't think its needed since I just cruise at 60mph.
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03-14-2019, 09:08 AM | #8 |
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Re: Mitchell transmission or overdrive
I ordered a 26% Mitchell two weeks ago for our Tudor with stock 3.78 rear end gearing. . I've had an old Borg Warner overdrive in the car since the late 1980's. Last fall the Borg Warner made a terrible clunk and then nothing. Permanent neutral. Tow truck ride back home. No more Borgs for us. Thanks for the great info guys! Makes me feel good about ordering a Mitchell.
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03-14-2019, 09:13 AM | #9 |
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Re: Mitchell transmission or overdrive
Have a 36% Mitchel for the cabriolet but also have a cut down Columbia in the '28 pickup with 3.78's and REALLY like being able to split the gears.
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03-14-2019, 03:24 PM | #10 |
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Re: Mitchell transmission or overdrive
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03-14-2019, 04:03 PM | #11 |
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Re: Mitchell transmission or overdrive
I'm sure I wouldn't be driving at that speed even with the higher ratio diff and without an O/D.
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03-14-2019, 05:44 PM | #12 |
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Re: Mitchell transmission or overdrive
A Model A has so much torque (125 ft lbs) relative to its weight that I can't see how splitting gears would be an advantage. The owner's manual wants you to get into high gear at 12 MPH.
I also agree that being able to cruise at 60 and better is not something that I would do without a modern brake and tire upgrade. These are great cars, but they have their limits.
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03-14-2019, 05:50 PM | #13 |
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Re: Mitchell transmission or overdrive
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03-14-2019, 05:52 PM | #14 |
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Re: Mitchell transmission or overdrive
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03-14-2019, 05:55 PM | #15 | |
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Re: Mitchell transmission or overdrive
Quote:
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03-14-2019, 06:23 PM | #16 |
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Re: Mitchell transmission or overdrive
If you do go with just the tranny, consider instead of a higher 1st and second, go with just the second. First is pretty high, especially for parades etc. Then there is a big jump to third. We opted to keep 1st as it is then a 15 percent higher second. Initial test drive, we liked it but winter hit before we could test it much.
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03-14-2019, 11:34 PM | #17 |
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Re: Mitchell transmission or overdrive
Bill, Is this with your Roadster or Town Sedan?
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03-14-2019, 11:41 PM | #18 |
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Re: Mitchell transmission or overdrive
Can we assume your engine is not stock? 3000 rpm is pretty high for a Model A engine.
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03-15-2019, 01:10 AM | #19 |
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Re: Mitchell transmission or overdrive
That is in the roadster.
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03-15-2019, 06:19 AM | #20 |
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Re: Mitchell transmission or overdrive
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03-15-2019, 06:47 AM | #21 |
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Re: Mitchell transmission or overdrive
I have been running a Mitchell Overdrive and 3:54 rear end gears in my coupe for a number of years. Great combo, recently had a Mitchell Transmission built but have not yet installed.
The overdrive/second is a sweet-spot for pulling hills where just second gear is too low. |
03-15-2019, 07:50 AM | #22 |
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Re: Mitchell transmission or overdrive
I have a 30's car because I enjoy traveling at 45 mph. If I wanted to go 60, then I would opt for a 50's car. I find that the 3.54 rear makes a nice drivable, near stock, car a pleasure to drive. Someone on here says that "speed is expensive, how fast do you want to go. I would add that speed kills when do you want to go. Jack
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03-15-2019, 08:17 AM | #23 |
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Re: Mitchell transmission or overdrive
Updating a model a to compete with today's drivers and road conditions is a challenge.To prove the car is still viable by modifying the original components is my goal with one.In no way is this an indictment of the car in stock form,we are here due to its enduring beauty.Geographic location often determines if you can enjoy your car stock,or modified..rural folks can do just about anything at 45,city folks have different demands based on conditions.Modifiers are not hotrodders..
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03-15-2019, 09:15 AM | #24 | |
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Re: Mitchell transmission or overdrive
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03-15-2019, 04:48 PM | #25 |
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Re: Mitchell transmission or overdrive
Final drive standard is 3.78:1 and second gear about 7:1.
At some speed you will likely be out of the power band in either gear. |
03-15-2019, 07:48 PM | #26 |
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Re: Mitchell transmission or overdrive
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03-16-2019, 09:29 PM | #27 |
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Re: Mitchell transmission or overdrive
Thank you all for your thoughtful responses they have given me a lot to think about. To the mix there is also the f150 4 speed conversion, it would be easy if there was only one choice. If I can ever come to a decision I’ll post the result.
Bill |
03-16-2019, 11:54 PM | #28 |
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Re: Mitchell transmission or overdrive
I have a coupe with a B engine and trans with synchros and a Laycock Overdrive; It handals flat and hills very well; I also have a sedan .an A engine dn draft weber and high compression head and a Laycock Overdrive with a 39 trans . Both cars are fun easy drivers with 3.78 rear ends and 600-16 wheels.
Some diff from Mitchell, when you want to shift into OD you just flip a switch on your gearshift and the same dn shifting from OD to 3rd. No clutch is required and your thrust bearings are minimized for wear. As for cons on the Laycock the biggest is you have to come out of OD before you put it in reverse or you can damage it. My Sedan with the 39 has a switch built on the Trans to cut out the OD when you put it into reverse; the Coupe does not have that feature. |
03-18-2019, 10:32 PM | #29 |
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Re: Mitchell transmission or overdrive
I run a 6.1 with the Mitchell 26 % in my 4door works very well hills or flat would recommend I have 2 other A s with mitchells these are stock heads and work well also
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03-24-2019, 10:45 AM | #30 |
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Re: Mitchell transmission or overdrive
The advantage with a Mitchell OD is not only a factor of speed but more importantly to smooth and quiet the motor. I found the Mitchell to be better balanced of the drive-line even when not traveling in overdrive. Also the motor does not "wind-up" so much when in OD, even at lower speeds. Quiets the motor and improves fuel economy.
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